It is generally known to form lightweight structural panels including a lightweight core structure sandwiched between two cover layers. The core structure typically is lightweight yet strong, because it has a configuration including hollow spaces as well as interconnected material webs or the like. Typical examples of such core structures include corrugated sheets, honeycomb cellular structures, and the like. Known core structures have a great variety of different configurations, and are made of a great variety of different materials.
The resulting composite structural panels, which respectively include such a core structure sandwiched and bonded between two cover layers, are used in many different applications, for example as lightweight structural panels or shell elements for walls, floors, and ceilings in transport aircraft, motor vehicles, ships, and trains. Such panels are similarly used in the interior and exterior construction of buildings. A further application of such composite structural panels is as filler panels or core panels of veneered furniture, for example, in the furniture manufacturing industry. Yet another application, especially in the case of corrugated cardboard panels, is the manufacture of crates, cartons, boxes and other packing materials from such composite structural panels.
Separately, it is known to form folded structures for various applications through the use of various different methods. These folding methods for folding sheet or web materials can be divided into intermittent or discontinuous processes, for example as described in U.S. Pat. No. 5,234,727, as well as continuous processes. Such continuous processes, in turn, can be divided into processes with a coupled or mutual lengthwise and crosswise contraction with a simultaneous expansion in the thickness direction of the starting material web (with a single-stage folding operation, for example as disclosed in U.S. Pat. No. 5,947,885), and processes in which the material web is first subjected to a crosswise contraction and is subsequently subjected to a deformation in the lengthwise direction of the material (in a two-stage folding operation, for example as disclosed in U.S. Pat. No. 4,012,932).
The continuous folding of long or essentially endless material webs necessarily involves an inexact deformation of the material in a mathematical and geometrical sense. Therefore, it is difficult, complicated, and costly to realize an actual mechanical apparatus that is to carry out the continuous folding of such a long material web in an exact manner, because a distortion or deformation of the material web arises, which may be within the deformation range of the elastic properties of the, material web and is difficult to control. In all of the above mentioned publications, the folding is carried out by a folding mechanism that accompanies the folding operation along the fold edges or the fold edges and surfaces.